While testing the hardness and crack resistance of the white aluminum oxide grinding wheel, the porosity and structural unevenness of the white corundum grinding wheel must also be tested. Therefore, in order to obtain more complete abrasive tool characteristics and better determine the cutting ability of the white aluminum oxide grinding wheel, it is possible to add pore volume size characteristics and their testing methods to the various white fused alumina grinding wheel quality indicators currently tested. The volume size characteristics of abrasive tool pores include several structural and quality indicators of the white aluminum oxide grinding wheel, such as the total pore volume, pore size, pore depth on the surface of the white corundum grinding wheel, and the distribution of pores in the white fused alumina grinding wheel. In order to test this new characteristic indicator, the corresponding testing instrument should be used.
The white aluminum oxide grinding wheel is a porous structure because there is an air layer in the mold material injected into the model, just like all loosely consolidated crystals. This air layer is compressed as the mold material is compacted during the green compaction. At this time, part of the air remains in the mold body after demolding to form pores. The other part of the air overflows from the mold material and forms channels or pore paths that connect the pores to each other and to the surface, thus forming the initial pores and pore path system.
Whether the pore system in the white aluminum oxide grinding wheel exists can be confirmed by the above permeability test of the abrasive blank. At this time, it is found that when the pressure is not supplemented, the permeability of the two ends of the abrasive is different, that is, the permeability of the compacted side is relatively small, while the permeability of the other side is relatively large. This is because the molded material on the compacted surface is pressed more tightly, so that the amount of air that comes out of the molded material on this end face is also more, thus reducing the number of pores. When the molded material is not stirred well or the molded material is unevenly distributed in some places in the model, the concentration of abrasive particles and binders will be uneven. When the blank is pressed, this phenomenon will lead to different compaction degrees in individual parts of the molded material, different amounts of extruded air, and the formation of pores and pore paths of different sizes. This is the unevenness of the structure of the white aluminum oxide grinding wheel. This phenomenon can be explained by the different permeabilities of various parts of the abrasive.
Various components of the binder, such as clay, talc, feldspar and water glass, all have compounds that can be burned out or evaporated at high temperatures. Therefore, during the sintering of the abrasive blank at a temperature of 1250-1300 degrees, the burned out and evaporated compounds form gas in the blank. This gas tries to expand under the influence of high temperature, and thus combines into a single space. Due to the inhalation of the newly generated gas, these spaces continue to increase, compacting the sintered binder to form pores. The gas space breaks through the binder at the thinnest part of the cross section and combines with other gas spaces to form a channel, namely the pore path.
